Mail problem, can't get new emails

I've set up "Mail" with a yahoo mail plus account, and it was alright before a week or so. I used to get new emails, send emails, and do everything really well untill last week. for some reason i just don't get any new emails, I don't get any alerts, I can't see them, I can't access them, i don't even have them in my inbox, no matter how many times i click "get mail" or "rebuild Mailbox".

when i accessed my mailbox from the yahoo mail website, I found that i got like 30+ new emails!

Look at your Inbox. Is there an icon to the right of it? If there is, then choose the Mailbox>Go Online item.

If you have more than one account setup in Mail, then sometimes one or more accounts may be offline while the other accounts remain online. Or you may want to temporarily take an account offline. In this case, choose Mailbox>Online Status>Take "{My Account}" Offline or Online, whichever the case may be.